50,000 years of Dreamtime

"...the occupation of Australia/New Guinea is momentous in that it demanded watercraft and provides by far the earliest evidence of their use in history. Not until about 30,000 years later (13,000 years ago) is there strong evidence of watercraft anyway else in the world, from the Mediterranean.Initially, archaeologists considered the possibility that the colonization of Australia/New Guinea was achieved accidentally by just a few people swept to sea while fishing on a raft near an Indonesian island. In an extreme scenario the first settlers are picture as having consisted of a single pregnant young woman carrying a male fetus. But believers in the fluke-colonization theory have been surprised by recent discovers that still other islands, lying to the east of New Guinea, were colonized soon after New Guinea itself, by around 35,000 years ago...." - page 42 of Guns, Germs and Steel The settlement of Australia is a breakthrough in the "human story." Very soon after anatomically modern humans began to replace (and to some extent assimilate) other lineages of our genus in Eurasia we pushed beyond the previous outer limits of the domains of humankind. The ancestors of Australian Aboriginals swept past the Wallace Line, and quickly settled the Ice Age continent of Sahul, consisting of Australia and Papua New Guinea. The biogeography of Australia is well known. Aside from bats and some endemic rodents the continent was free of placental mammals before modern humans arrived. As for when these humans made landfall, there is some debate as to that particular issue. The oldest remains from Australia, Mungo Man, has been dated to anywhere between 70,000, and 30,000, years before the present. If we took the older date then Australia would have been settled almost immediately after the expansion of non-African modern humanity. If we accepted the younger date, then the settlement of Australia would have been concurrent with the final replacement of Neandertals by modern humans in Europe. The current consensus seems to be that Mungo Man dates to approximately 46,000 years before the present. As the first dating of a particular individual from a species in a region is liable to miss earlier individuals who were not fossilized it seems likely that Australia was settled by anatomically modern humans on the order of 46,000 years before the present, but somewhat earlier than that date. That would imply that Australia was populated by anatomically modern humans at least 10,000 years before Europe. One should probably not be too surprised by this. Out-of-Africa humans were probably initially tropically adapted so lateral migration would have been easier, but also, there were no hominin competitors in Australia. But how do these archaeological insights relate to the current Aboriginal population of Australia? Such questions are fraught with politics, but let's put that to the side. We know that Australia was not totally isolated from the rest of the world. The dingo arrived from Southeast Asia within the last 4,000 years. The Aboriginals of northern Australia were certainly familiar with the idea of agriculture, because they traded with the Torres Straits Islanders, who were farmers and seafarers, and who had contacts with New Guinea (see After the Ice). Some anthropologists, such as Joseph Birdsell, proposed that modern Aboriginals were a compound of multiple migration events, and had undergone a great deal of evolution in situ. Additionally, classically trained physical anthropologists in the early 20th century noted morphological parallels between Australian Aboriginals and the peoples of India, giving rise to the construct of the Australoid race (a term still used by Indian anthropologists). As I noted earlier the connection between South Asia and Australia genetically seems likely to be distant and tenuous at best, inferring from what we know of uniparental markers (genetic variants passed only through the mother or father, the mtDNA and Y). The genetic data tentatively seem to reject Birdsell's model, and favor a more parsimonious one of a single original settlement on Sahul, and subsequent diversification and isolation (Australia, Tasmania and Papua New Guinea were separated only ~10,000 years ago with rising sea levels). But there's only so much that uniparental lineages can tell us. There are limits to the information one can glean from relatively short sequences of mtDNA and Y, and, these gene lineages are subject to their own particular dynamics. Not only do human mating patterns exhibit sex-specific biases, but the neutrality of these lineages from an evolutionary perspective has been questioned. And, the haploid nature of these loci also mean that the effective population size is small (i.e., only copy of each per person, instead of two as in the case of most genes) and stochastic fluctuations may be more extreme than in the rest of the genome. On the one hand more random variation could allow for the emergence of greater between population differences which might be informative, but on the other hand it can also swamp out the past history too quickly and result in convergences which tell us nothing about phylogenetic connections.